In present day typewriters, dot matrix serial printers, and dot matrix line printers, it is common practice to include a ribbon cassette having a continuous one-piece ribbon that is moved past the print hammers during printing. It is also common practice for the ribbon cassettes to contain an ink reservoir that either periodically or continuously re-inks the ribbon. The ink reservoirs are generally located in contact with a transfer roller that, in turn, contacts the ribbon as the ribbon enters the cassette after it moves between the print hammers and paper. Typically, as the ribbon enters the cassette, ink flows the ink reservoir onto the surface of a transfer roller and then onto the ribbon.
Some ribbon cassettes store the ribbon within the cassette in a random fashion. The ribbon is unfolded from such cassettes as the ribbon exits the cassette. Upon reentering the ribbon cassette, after passing in front of the print hammers, the ribbon is re-inked prior to being randomly folded. Such ribbons often have a Mobius loop configuration, which allows the print hammers to equally impact both sides of the ribbon. This configuration tends to increase ribbon life by decreasing ribbon wear.
As a ribbon's useful lifetime has been extended due to improvements in materials, etc., it has become more important to properly and effectively re-ink the ribbon in order to obtain good quality print throughout the life of the ribbon. In the past, ink reservoirs have typically been formed of an open cell material such as a foam or sponge. Open cell materials are capable of absorbing large quantities of ink while allowing the ink to flow freely from the surface of the ink reservoir onto the transfer roller and, in turn, onto the ribbon as the ribbon contacts the transfer roller.
In addition to allowing ink to flow from the surface of the ink reservoir onto the transfer roller, open cell materials also allow ink to move freely within the reservoir. This leads to a disadvantage. Specifically, because ink flows freely within the open cell materials used to form the ink reservoir, gravity causes ink to pool in the lower portion of the ink reservoir. Thus, the density of the ink at the bottom of the reservoir is greater than at the top. This reservior ink gradient results in a greater flow of ink onto the lower portion of the transfer roller than the upper portion. Consequently, more ink is transferred to the lower portion of the ribbon. If the ribbon is contained within the case in a Mobius loop, after more than one revolution of the ribbon, more ink is transferred to the upper and lower portions of the ribbon than the center.
In the case of a dot matrix serial printer, the upper and lower portions of a character printed with a ribbon that has been re-inked using prior art re-inking mechanisms of the type described above has a denser ink distribution than the center portion. Because such print is darker and more defined at the top and bottom than at the center, print quality is less than desired. In the case of dot matrix line printers, the ribbon is generally oriented in front of the print hammers such that one edge of the row of hammers contacts the bottom of the ribbon while the other edge of the row of hammers contacts the top of the ribbon. This configuration allows different hammers to contact different sections of the ribbon, thus decreasing ribbon wear. The print of a line printer using a ribbon re-inked using prior art re-inking mechanisms shows that a lower print density is produced at the center of the page than at the edges, thus reducing print quality.
Therefore, there exists a need for a new type of ink reservoir that is capable of maintaining an even distribution of ink supplied to the transfer roller. This will result in an even distribution of ink being transferred from the transfer roller to the ribbon as the ribbon contacts the transfer roller. An even distribution of ink over the width of the ribbon will, in turn, result in improved print quality.